How much further could steam have progressed?

[carnej1]

Here’s an interesting question. Had the diesel not come along, how much further could steam technology have progressed? What would have come after the 4-8-4? I know the Russians tried building a 4-14-4 and it was quite the epic fail. Realistically, a 4-10-4 would be the largest practical passenger locomotive US rails could handle.

We have recently has several long and very detailed discussion threads on this very subject over in the “Steam & Preservation” Forum on this site which you may find interesting.

This is the most recent one:

http://cs.trains.com/trn/f/740/t/213219.aspx